Flex cable connector for cryogenic application

ABSTRACT

A new electrical cryogenic connector system employs two printed circuit board type mating connectors (1 &amp; 3), each containing a plurality of plated-on metal lines (5 &amp; 6) running along the respective circuit boards in parallel, with the plated-on metal lines on at least one of the connectors being of Beryllium Copper material. The ends of the series of Beryllium Copper lines on one of the complementary circuit boards is formed into a pointed spring finger that is pointed toward the opposed circuit board. With the two boards sandwiched and pressed together with their plated on metal lines directly in line with and facing one another, the spring fingers compress and, under the spring force created by that compression, the spring fingers engage and maintain positive electrical contact with the corresponding conductor traces on the opposed circuit board. Ancillary to the described connector, a new method for constructing an electrical connector is also presented.

STATEMENT OF GOVERNMENT SUPPORT

This invention was conceived during the course of Contract orSubcontract No. ATSP FQ406-95-D-0069, D.O. 0015 for the Department ofDefense. The government has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates to electrical connectors, and, more particularly,to a flex cable connector system useful in cryogenic environments.

BACKGROUND

A number of companies, such as IBM and Packard-Hughes, produce highdensity flexible electrical cables, often referred to as "flex cable",for use in routing electronic data. These cables have the capability ofrouting data at high rates of up to Gigabits per second. The cable isrelatively flat and resembles a thick stiff belt in appearance and itmay be bent around corners or wrapped, much like an ordinary leatherbelt. The flex cables pack a large number of separate insulatedelectrical lines within the flex cable's limited width, typically at aline density greater than eighty signal lines per inch. In itsconstruction, the flex cables employ a polyimide film, a strong flexibleplastic insulating material, as the dielectric substrate and outerinsulating wrap. The electrical lines are lithographically defined andare formed of a very thin and narrow metal strips upon the dielectricsubstrate and a covering layer of the same material is laminated to thatsubstrate covering the metal strips.

The foregoing flex cables may be designed to have low thermalconductivity, a characteristic which makes the cable ideal for cryogenicapplications. The cables can be used to connect cryogenic electronicsapparatus, superconducting electronic apparatus, cryo-CMOS circuits andcooled GaAs amplifiers, which a cryogenic refrigeration system maintainsat very low cryogenic temperatures during operation, to other externalelectronic components and circuits that are maintained at roomtemperature. Since the cable doesn't conduct significant external heatto the cryogenic apparatus, the cable does not create an undue heat loadon the cryogenic refrigeration system.

For expeditious cable connection and/or disconnection, electricalconnectors are employed with the cable. Respective lengths of cable arewired into respective electrical connectors and the lengths of cable areinterconnected by connecting the two mating electrical connectorstogether, as is conventional practice in the electronic field.

As is elementary, an electrical connector contains a sufficient numberof spaced electrical contacts, enabling each connector contact to beelectrically connected to a respective electrical lead in the cable. Acable to cable connection is made by mating two connectors or connectorportions, as variously termed, together, to form the connector system orconnection, and bridging the multiple electrical paths from one cable toanother through the connector contacts. To avoid possible confusion inthis description, it is appropriate to remind the reader that eachmating half or portion of a connector is customarily also referred to asa connector. When reference is made to connector, thus, the readershould be certain to understand the context in which the reference ismade to understand whether reference is being made to a connectorportion or to the connector system.

The electrical connectors used by the afore-recited flex cablemanufacturers to connect flex cables together or to connect flex cablesto rigid printed circuit boards employ a "pressed contact" arrangement.The pressed contact arrangement is not the typical male-female prong andsocket contact arrangement found in conventional electrical connectors,in which a prong contact frictionally engages within a socket contact.Instead, in the situation in which two flex cables are to be joined, twosubstantially identical relatively planar thick rigid printed circuitboards, containing the requisite number of electrical lines formedslightly protruding above the circuit board's planar surface serve asthe mating connectors. And, in the situation in which a flex cable is tobe connected to a printed circuit board, the flex cable and the rigidprinted circuit board, containing the requisite number of electricallines protruding slightly above the planar surface of the circuit board,serve as the mating connectors.

As those skilled in the art appreciate, for a cable to cable connection,the electrical lines plated upon each of those circuit boards is alignedand soldered or otherwise joined to corresponding electrical leads at anend of an associated flex cable, typically by conventional solderingtechniques. One of the circuit boards in the connector is invertedrelative to the other and, with the electrical lines on the circuitboards aligned, the boards are pressed into engagement to place therespective lines in electrical contact and form the electricalconnection. To complete the connector, a mechanical fastening system,including alignment pins and a pressure pad of elastomeric materialclamps the mated connector portions together and maintains therespective parallel conductors in contact under a positive pressure orforce. The surface of pressure pad contains a series of minute elasticrubber-like bumps or fingers to press against the top of one of thecircuit boards, providing, thus, the pressed contact arrangement.

Although the foregoing connector design serves well at room temperature,at cryogenic temperature the connector, and, particularly, theconnector's elastomeric pad, often fails to function properly. Atcryogenic temperature, the elastomeric material forming the pressurepads becomes brittle and loses its ability to maintain adequate pressureon the circuit boards. As example, where the connector connects eightyor so electrical lines in a high density flex cable, should any one ofthose electrical lines fail to connect through the connector to anassociated line, the connector is deemed to have failed. The loss of anyelectrical path through the connector cannot be tolerated. Thus,although available flex cable is ideal for application in cryogenicdevices, presently available connectors for those flex cables areunsuited for use at those very low temperatures.

When the foregoing connector fails, it must be replaced. To do sorequires the cable to be disconnected from the old structure andreattached and soldered to the replacement or requires a new cable to beattached and soldered. In addition to requiring new connectors, thatprocedure also requires considerable time and expense.

An object of the present invention, therefore, is to provide a newconnector system for flex cable that functions at cryogenictemperatures.

A further object of the invention is to provide a connector system thatmay be easily repaired or reconstructed, without requiring cablerewiring anew, should the connector system fail.

Another object of the invention is to provide a connector system thatadapts flex cables to cryogenic device application and may be used incryogenic systems.

And a still further object of the invention is to provide a positivepressure contact type connector that does not incorporate elastomericmaterial or any other material that becomes brittle or disfunctional atcryogenic temperatures.

SUMMARY OF THE INVENTION

In accordance with the foregoing objects, the present invention employstwo printed circuit board type connector components or connectors. Oneof those printed circuit board elements contains a plurality ofplated-on bare Beryllium Copper lines that extend along the boardalongside one another in parallel, and serve as the connector'scontacts. The second printed circuit board contains a like plurality ofplated-on metal lines similarly extending alongside one another. An endportion of the Beryllium Copper lines is detached from the board'ssurface and permanently deformed or shaped into a concave curve, thatcurves outwardly from the board surface. Due to the nature of BerylliumCopper, the curved portions are resilient and form electricallyconductive spring fingers. Preferably, the end edge of each springfinger is pointed.

With the boards facing one another, aligned, and squeezed together, thespring fingers on the one circuit board are compressed and press againsta corresponding metal line on the other printed circuit board tocomplete an electrical path through the connector. Even at cryogenictemperatures, the is spring tension in the compressed springs ensurespositive electrical contact between each pair of lines in theconnector's mating halves. In repeated use, the connector is notadversely affected by continued recycling between cryogenic temperaturesand room temperatures.

A novel process to fabricate the connectors, particularly toconstruction of the spring fingers, is also described. That processincludes plating the rows of conductors on the printed circuit board,cutting end portions of those conductors away from the circuit board tofree the end portions, bending those end portions over a cylindricalmandrel to permanently deform those end portions into a curved shapewith spring like characteristics, and pressing the deformed ends downagainst the circuit board to define the final curved shape to the springfingers.

The foregoing and additional objects and advantages of the inventiontogether with the structure characteristic thereof, which was onlybriefly summarized in the foregoing passages, becomes more apparent tothose skilled in the art upon reading the detailed description of apreferred embodiment, which follows in this specification, takentogether with the illustration thereof presented in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a general pictorial view of the an embodiment of the connectorsystem containing the mating connectors;

FIG. 2 is a general pictorial view of the connector system assembled;

FIG. 3 is a more detailed top plan view of one connector of theconnector system, drawn to a larger scale;

FIG. 4 is a side view of the embodiment of FIG. 3;

FIG. 5 illustrates a portion of the elements of the embodiment of FIGS.3 and 4 in top plan view and FIG. 6 illustrates FIG. 5 in side view;

FIG. 7 is a partial section view taken along the lines 7--7 in FIG. 4and drawn to a larger scale;

FIGS. 8, 9 and 10 illustrate both mating connectors in side view; theadditional clamping elements to form a connector system, and therelationship of the two mating connectors as assembled into a cable tocable connector system;

FIG. 11 illustrates a cable to circuit board embodiment of the connectorsystem; and

FIG. 12 illustrates the process of forming the spring fingers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is made to FIGS. 1 and 2, which pictorially illustrate inminimal detail the principal elements of the disclosed electricalconnector or, as variously termed, electrical connector system, as usedto form a cable to cable connection. Referring first to FIG. 1, theconnector system contains two connector portions, a male connector 1, tothe left, and a female connector 3 to the right. The male connectorcontains multiple parallel Beryllium Copper traces, lines, or, asvariously termed, contacts 5, located spaced apart, attached to, or moreaccurately, plated upon the upper surface of a relatively rigid printedcircuit board 7. The circuit board is formed of standard insulatingmaterial, is an electrical insulator, and is at least semi-rigidphysically.

As generally illustrated the ends of each Beryllium Copper contact isdetached from the board and is of a curved shape that curves upwardlyfrom the circuit board's surface. Importantly, such free end possesses aspring like characteristic. The opposite end of the parallel conductorarrangement, which remains connected to the circuit board, is connectedto corresponding metal lines or conductors in a flex cable 9, partiallyillustrated.

The mating connector 3 contains the series of metal conductors 6 platedon the surface of a like constructed printed circuit board 8; and theends of those conductors are connected to corresponding conductors inanother flex cable 10, partially illustrated. However, in this matingconnector, the entire length of conductors 6 lie flat on the uppersurface of the supporting circuit board 8. Conductors 6 may be anyelectrically conductive metal such as copper, tin, gold, gold-platedcopper, aluminum or, if desired, Beryllium Copper.

When the connectors are to be mated, as shown in FIG. 2, the printedcircuit boards 1 and 3 are placed one atop the other, with printedcircuit board 6 inverted so that the bare conductors on the two circuitboards directly face one another, and the two circuit boards arefastened together in that relationship by suitable fastening means, onlygenerally represented in this figure by bolts 12. It is appreciated,that, when assembled together as illustrated in FIG. 2, the completedconnector serves to provide an electrical path through the connector foreach of the electrical lines in the associated cables.

The foregoing pictorial illustrations serve to generally introduce thenew connector structure and illustrate its general design principleusing a limited number of electrical contacts and with limitedconstruction details. A more complete detailed illustration of apractical embodiment of the invention is provided in the succeedingdrawing figures, which are next considered. For convenience in thefollowing figures, the same number designation is given to an elementthat corresponds to an element previously identified in FIGS. 1 and 2.

A more detailed view of the male connector 1 is illustrated to adifferent scale in top plan view in FIG. 3 and in side view in FIG. 4 towhich reference is made. Circuit board 7 is wide enough to accommodatethe number of contacts 5 carried on its surface. A rectangular shapedmetal stress relief clamp component on the upper side and acomplementary rectangular shaped metal stress relief clamp 17, on theunderside, are joined by a pair of threaded bolts 18. The bolts fitthrough bolt passages or holes formed in the upper clamp, and on theouter edges of the circuit board and extend into threaded holes in themating relief claim 17.

With the respective bolts screwed into clamp member 17 and tightened,the relief clamps compress and hold an end portion of flex cable 9,leaving an end portion of the flex cable, containing the formed springfingers, exposed at the front end of the clamp. A pair of circularpassages 14 are located along the left and right edges of the circuitboard. Those passages form alignment holes, which are used whenassembling the male connector to it mating female connector as laterherein described in connection with FIGS. 8-10. The outwardly curved endor spring finger that forms an extension to each of the conductors ismore visible in the side view of FIG. 4.

The basic component of the connector of FIG. 3 is illustrated in FIG. 5in top plan view and in FIG. 6 in side section view to which referenceis made. The two passages 13 for bolts 18 are visible in this figure.The conductors 5 are formed in parallel and occupy a portion of theupper surface of circuit board 7, protruding slightly above the circuitboards insulating surface. The bond between the conductors 5 and thesurface of the circuit board is broken at the front end of theconductors and extends rearward a short distance, about to the positionof dash line 11. The detached portions or, as variously termed, freeends are permanently deformed into a curve as illustrated in FIG. 6,forming spring fingers. The tip ends of those spring fingers,preferably, each come to a point.

Returning to FIG. 3, flex cable 9, partially illustrated, is a typicalhigh density cable. It suitably contains 128 parallel electrical linesor, as variously termed, signal traces 20 that are of three mils linewidth on an eight mil pitch laminated between thin layers 19 and 21 ofpolyimide. The corresponding relatively rigid circuit board 7 contains alike number of lines or traces 5 of like width and pitch. To give abetter feel to the small sizes possible for the connector invention, itis noted that in a practical embodiment of the connector of FIGS. 3 and4, the width of the connector, along the width of the figure, is about1.33 inches, and the height or length of the connector, along thevertical direction in the figure is about 0.7 inches.

The cable is attached to the printed circuit board and the individualleads are connected to associated electrical leads on that circuitboard. That attachment is accomplished by conventional solderingtechnique. As illustrated in the enlarged partial side view of FIG. 7,which is taken along line 7--7 in FIG. 4, flex cable 9 contains outerinsulating layers 19 and 21 with the electrical conductors 20 sandwichedand laminated in between. A short length of the underside coveringpolyimide layer 21 is removed from an end of the cable to expose theelectrical leads 20, the upper covering layer 19 remaining unchanged.The exposed electrical leads 20 are then aligned with the correspondingelectrical leads 5 on the circuit board; and solder is applied tomechanically and electrically join leads 5 and lines 20 together.

The mating female connector contains the same elements, located in thesame orientation, having the same relationship and is fabricated in thesame way as the male connector, except that its plated-on connectorconductors lie entirely flat on the supporting circuit board, such aswas generally illustrated at 6 in FIG. 1, and do not form springfingers. Hence the view of the mating connector is the same as presentedin FIGS. 3 and 4, with the exception that the end of the supportedconductors do not curve upward, as does conductor 5, but lies flat onthe circuit board. Accordingly, the structure of the mating femaleconnector need not be separately illustrated.

The described connector components are assembled together to complete aconnection as illustrated in the side assembly views presented in FIGS.8, 9 and 10 to which reference is made. The female connector 3 includesa strain relief bar 22, which corresponds to relief bar 15, a secondrelief bar 24, which corresponds to relief bar 17, and a pair of bolts26, corresponding to the pair of bolts 18 in the male connector 1. Italso includes a corresponding pair of alignment passages 16. As shown inFIG. 8, the connector components 1 and 3, previously assembled torespective cables 9 and 10, are arranged one over the other with thealignment holes 14 underlying the corresponding alignment holes 16 infemale connector 3. As shown in FIG. 9, connector 3 is brought intocontact with connector 1 so that the conductive spring fingers at thetip end of conductor s 5 of connector 1 contact the correspondingconductors 6 on circuit board 8, and commences to compress those springfingers against conductors 6. When completed the spring fingers arealmost flattened, as illustrated in FIG. 10, but retain their resiliencyand exert a positive reactionary force ensuring good contact pressure.

To hold the elements in the foregoing mating relationship and completethe connector a fastening structure is used that clamps the matingconnectors together. That clamping force also maintains the springcontacts under a positive pressure or force. Such a clamp is formed withupper and lower clamping bars 23 and 25, and a pair of bolts 27 and nuts29, one from each of the pair being located on opposite ends of theclamping bars. Each of the clamp bars is of a straight narrow flatrectangular box shape, as illustrated in end view in the figure, and isof a length that extends across the width of the connector.

Upper and lower clamp bars 23 and 25 are placed in contact with therespective rear surfaces of the circuit boards of connectors 3 and 1,respectively, with the alignment or bolt holes in the clamping barsplaced in alignment with the corresponding alignment holes 14 and 16 ineach of those circuit boards. Bolts 27, only one of which isillustrated, are inserted through the holes and are fastened in placewith nuts 29, only one of which is illustrated. The fastened boltsthereby maintain the components in the illustrated sandwichedrelationship. The bolts and nuts exert force on the adjacent clampingbars, and the bars distribute such clamping force across the entireunderlying surface.

Preferably a portion of the bolt's shank leading from the bolt head isleft unthreaded, leaving a smooth cylindrical surface of a diameter justsmall enough to clear the cylindrical walls of the alignment holes inthe circuit boards and interposer. The foregoing structural featureallows the fastening bolt to serve also the function of an alignment pinthat ensures that the parts remain in the desired alignment throughfinal assembly.

The foregoing embodiment was of a cable to cable connection. It isappreciated that the connector also may be used for a cable to circuitboard connection. In such an alternative, the circuit board that servedas a base to a mating connector, such as circuit boards 7 or 8 is notconnected to a flex cable, but instead constitutes a portion of thecircuit board of a particular electronic apparatus. That is, the circuitboards connector conductors are applied to an edge region of theapparatus's circuit board, and the rear end of those conductors arerouted by means of other plated on metal conductors to the variouscircuit elements found on the board, which is in lieu of a flex cableconnection to those elements.

Such an alternative embodiment is illustrated in side view in FIG. 11showing the connector system with the two connectors assembled together.In as much as most of the elements of the alternative connector systemare identical to the corresponding elements in the prior embodiment,and, some, though not physically identically are functionally identicalto corresponding elements in the prior embodiment, the correspondingelements of this embodiment are denominated in the figure by the samenumber used for the element in the prior embodiment and primed. It isappreciated that the description of the elements for this embodiment isthe same as that already given with respect to the prior embodiment,which need not be repeated.

In this embodiment, the female connector 3' is of the same constructionillustrated in FIGS. 8, 9 and 10. However, the male connector 1' isformed on an edge of the equipment's printed circuit board 7', whichsubstitutes for the circuit board 7 in the prior embodiment. Thatequipment circuit board contains appropriate alignment holes. And theassociated clamping device 23', 25', 27' and 29', is the same as in theconnector structure earlier described. Since the male connector does notattach to a cable, the cable strain relief elements used in theembodiment of FIGS. 8-10 are not necessary. The spring finger ends toBeryllium Copper conductors 5' are illustrated in FIG. 11 in thecompressed condition. Prior to final assembly, those spring fingersappear the same as the corresponding spring fingers of conductor 5 ineach of FIGS. 8 and 9.

The procedure to fabricate the spring fingers was earlier only brieflydescribed. Considering that procedure in greater detail and referring asnecessary to FIG. 12 illustrating the steps, the procedure starts withstandard printed circuit board material, as example that known as FR-4containing a plated on layer, suitably two mils thick, of full hardBeryllium Copper sheet. Beryllium Copper is a known alloy containingboth metal elements homogenously mixed and known to be a good electricalconductor, not the best, is hard and durable and is known to be usefulfor manufacture of spring fingers. The material has been proposed foruse in various electrical devices including electrical connectors, whereits physical and electrical characteristics best serve the needs of theelectrical device.

The foregoing plated circuit board is then treated to form the lengthsof conductor desired for conductors 5, suitably by a conventionalsubtractive etching process known in the industry. In this the BerylliumCopper surface is coated with photoresist and exposed photographicallyto a negative image of the desired conductors ultimately desired,including, preferably a pointed end to those conductors, the unexposedphotoresist is chemically removed, exposing the unwanted metal portions,and board is placed in a chemical etchant bath, suitably Ferric Choride,to etch away the unwanted metal. Thereafter the cured photoresist isremoved, leaving the formed conductors 5 as generally illustrated at 31.

The bond between conductors 5 and circuit board 7 is then manuallybroken, suitably by carefully cutting into the board under the tip endsof the conductors, one by one, with a sharp Exacto knife or equivalent,a somewhat labor intensive step, illustrated at 32. This procedurereleases a small portion of the length of conductor 5, freeing the ends.Then a long cylindrical mandrel is placed atop and transverse theconductors 5 a short distance from the conductor's tip end at thelocation where the bend is to be formed.

With the mandrel held in place, a straight flat stiff metal forming baris slipped underneath the tip ends of the conductors. The forming bar isrotated to scoop up all the tip ends and then press them against thecylindrical mandrel, exceeding the elastic limit to the material, as at33. This permanently deforms the shape of the free ends and produces theinitial bend in the conductor's free ends.

Next, the mandrel and forming bar are removed. With that somespring-back occurs, but the Beryllium Copper strips remain permanentlydeformed. The forming bar is reapplied to the free ends of theconductors and is pressed down, as at 34, and then released. This latterstep defines the final curved shape of the conductor's free ends, thespring fingers, as represented at 35.

The connector remains effective at cryogenic temperatures. When cooledall of the metal parts contract with temperature as would enhance firmelectrical contact between the elements. When the equipment is to bedisengaged and removed, the cryogenic temperatures are removed and theunit is brought back to room temperature. The connector is easilydisassembled by unfastening the nut, removing the clamping structure anddetaching the component elements, in essentially a reverse procedure tothat earlier described in connection with assembly in FIGS. 8 through10. It is found that the spring fingers retain their springiness evenafter cycling through cryogenic temperatures and back and that theconnector elements may then be reused.

The connector system is a simple structural and may be constructedalmost entirely by automated fabrication equipment, making the systemrelatively inexpensive. Instead of requiring substitution of a newconnector and the attendant labor of rewiring a new connector to thecable, great savings in both time and effort are thereby achieved.

As those skilled in the art appreciate, many modifications to theforegoing structure are permissible without departing from the scope ofthe present invention. The foregoing embodiments used contacts that arepointed in shape. However, as those skilled in the art understand fromreading this specification, the connector invention is not so limited.Other shapes, though less preferable, may be substituted, and achievesome benefit of the invention. Additionally, the preferred embodimenthas been illustrated in connection with connectors having very finetraces and using very minute sized contacts as exist for a particularcryogenic application known to the inventors, which gave rise to theproblem solved by the disclosed connector. However, it is recognizedthat the disclosed connector structure may be adapted to larger orsmaller size metal traces in the same or for different applications andmay find application in other fields for related reasons.

Lastly, the Beryllium Copper spring contacts for the embodiment werefabricated using a particular process that used a cutting tool. Otherfabrication processes might hereafter become available that can besubstituted.

It is believed that the foregoing description of the preferredembodiments of the invention is sufficient in detail to enable oneskilled in the art to make and use the invention. However, it isexpressly understood that the detail of the elements presented for theforegoing purpose is not intended to limit the scope of the invention,in as much as equivalents to those elements and other modificationsthereof, all of which come within the scope of the invention, willbecome apparent to those skilled in the art upon reading thisspecification. Thus the invention is to be broadly construed within thefull scope of the appended claims.

What is claimed is:
 1. An electrical cryogenic connector for a flexcable comprising:a first base of electrically insulative material havinga plurality of spaced Beryllium Copper conductors attached to andprotruding above a first surface of said base, said Beryllium Copperconductors being oriented in parallel; a second base of electricallyinsulative material having a plurality of spaced metal conductorsattached to and protruding above a first surface of said second base,said metal conductors being oriented in parallel; said Beryllium Copperconductors on said first base having an end portion detached from saidbase and configured in a curved geometry that curves outwardly from saidfirst surface of said first base to define a spring finger; said firstand second bases being oriented with said conductors directly facing oneanother, with each said conductor on one of said bases aligned inparallel with a corresponding one of said conductors on the other ofsaid bases; and fastening means for fastening said first and secondbases in sandwiched relationship to compress said spring fingers,wherein said spring fingers engage a corresponding one of said pluralityof metal conductors on said second base and maintains a positive contactpressure therewith.
 2. The invention as defined in claim 1, wherein anend of each of said spring fingers is pointed.
 3. The invention asdefined in claim 1, wherein said first base includes a pair of spacedalignment holes; wherein said second base includes a pair of spacedalignment holes, said alignment holes in each said pair being spacedapart a predetermined distance; and wherein a first alignment hole ineach pair is axially aligned with a corresponding first alignment holein each of the remaining pairs of alignment holes; and wherein a secondalignment hole in each pair is axially aligned with a correspondingsecond alignment hole in each of the remaining pairs of alignment holes.4. The invention as defined in claim 3, wherein said fastening meansfurther comprises:a first clamping bar and a second clamping bar, saidfirst clamping bar abutting a rear surface of said first base and saidsecond clamping bar abutting a rear surface of said second base; andfirst and second bolt means extending through said first clamping bar,through said alignment holes and into engagement with said secondclamping bar.
 5. An electrical cryogenic connector for cryogenicapplication comprising:a first printed circuit board of electricallyinsulative material having a plurality of spaced flat spring metalelectrical conductors attached in parallel orientation to and protrudingfrom a first surface of said first printed circuit board, said spacedflat spring metal electrical conductors comprising thin strips platedonto said first surface; said spaced flat spring metal electricalconductors on said first printed circuit board including respective endportions detached from said base and formed in a curved shaped extendingoutwardly from said first circuit board to define spring fingers.
 6. Theinvention as defined in claim 5, wherein said first printed circuitboard further includes a pair of spaced alignment holes; and, furthercomprising:fastening means for mechanically holding said first printedcircuit board in mating engagement with another printed circuit boardcontaining a plurality of like-spaced plated-on conductors, wherein saidspring fingers respectively engage corresponding conductors on saidmating circuit board and maintains positive contact pressure therewithat cryogenic temperature, said fastening means including: a firstclamping bar and a second clamping bar; said first clamping bar forabutting a rear surface of said first printed circuit board and saidsecond clamping bar for abutting a rear surface of said another printedcircuit board; and first and second bolt means for extending throughsaid alignment holes and joining said clamping bars.
 7. The invention asdefined in claim 5, wherein said spring metal consists of a BerylliumCopper alloy.
 8. The invention as defined in claim 6, furthercomprising:a flex cable having an end, said flex cable containing aplurality of electrical lines arranged in parallel along a common planesandwiched between first and second covering layers of electricalinsulating material; said second covering layer extending to apredetermined distance of said end, leaving an end portion of saidelectrical lines uncovered; said end portion of said electrical linesoverlaying portions of and being mechanically and electrically connectedto corresponding ones of said spaced flat spring metal electricalconductors for providing electrical contact with said respectivecorresponding ones of said spaced flat spring metal electricalconductors.
 9. The invention as defined in claim 8, furthercomprising:strain relief clamping means for clamping said flex cablemeans to said first printed circuit board, said clamping means beingmounted over said flex cable means and before said end portion of saidflex cable means.
 10. An electrical connector for cryogenic applicationcomprising:a first printed circuit board of electrically insulativematerial having a plurality of spaced flat spring metal electricalconductors attached in parallel orientation to and protruding from afirst surface of said first printed circuit board, said spaced flatspring metal electrical conductors comprising thin strips plated ontosaid first surface; said spaced flat spring metal electrical conductorson said first printed circuit board having an end portion detached fromsaid base and formed in a curved shaped extending outwardly from saidfirst circuit board to define spring fingers; said first printed circuitboard further including a pair of spaced alignment holes; and, furthercomprising: fastening means for mechanically holding said first printedcircuit board in mating engagement with another printed circuit boardcontaining a plurality of like-spaced plated-on conductors, wherein saidspring fingers respectively engage corresponding conductors on saidmating circuit board and maintains positive contact pressure therewithat cryogenic temperature, said fastening means including: a firstclamping bar and a second clamping bar; said first clamping bar forabutting a rear surface of said first printed circuit board and saidsecond clamping bar for abutting a rear surface of said another printedcircuit board; and first and second bolt means for extending throughsaid alignment holes and joining said clamping bars; said electricalconnector further comprising: flex cable means having an end, said flexcable means containing a plurality of electrical lines arranged inparallel along a common plane sandwiched between first and secondcovering layers of electrical insulating material; said second coveringlayer extending to a predetermined distance of said end, leaving an endportion of said electrical lines free of electrical insulating material;said end portion of said electrical lines overlaying portions of andbeing mechanically and electrically connected to corresponding ones ofsaid spaced flat spring metal electrical conductors for providingelectrical contact with said respective corresponding ones of saidspaced flat spring metal electrical conductors; strain relief clampingmeans for clamping said flex cable means to said first printed circuitboard, said clamping means being mounted over said flex cable means andbefore said end portion of said flex cable means; said first printedcircuit board including first and second strain relief bolt passages,said first and second strain relief bolt passages being spaced apart;and wherein said strain relief clamping means further comprises: a firststrain relief clamping bar and a second strain relief clamping bar; saidfirst strain relief clamping bar including a pair of bolt passages, saidbolt passages being spaced apart the same distance as said first andsecond strain relief bolt passages; said second strain relief clampingbar including a pair of threaded bolt holes, said bolt holes beingspaced apart the same distance as said first and second strain reliefbolt passages; said first strain relief clamping bar for abutting saidflex cable means and said second strain relief clamping bar for abuttinga rear surface of said first printed circuit board; first strain reliefbolt means for extending through one of said pair of bolt passages insaid first strain relief clamping bar, said first strain relief boltpassage, and into threaded engagement with one of said pair of threadedbolt holes; and second strain relief bolt means for extending throughanother one of said pair of bolt passages in said first strain reliefclamping bar, said second strain relief bolt passage, and into threadedengagement with another one of said pair of threaded bolt holes.
 11. Anelectrical connector for cryogenic application comprising:a firstprinted circuit board of electrical insulator material having aplurality of spaced Beryllium Copper conductors attached in parallelorientation to and protruding from a first surface of said first printedcircuit board, said spaced Beryllium Copper conductors comprising thinstrips plated onto said first surface; said spaced Beryllium Copperconductors on said first printed circuit board having a pointed endportion detached from said base and formed in a curved shaped extendingoutwardly from said first circuit board to define spring fingers; saidfirst printed circuit board further including a pair of spaced alignmentholes; a second printed circuit board of electrical insulator materialhaving a plurality of spaced metal conductors attached in parallel toand protruding from a first surface of said second printed circuitboard; said second printed circuit board further including a pair ofalignment holes spaced apart by the same distance as said pair ofalignment holes in said first printed circuit board; said plurality ofspaced metal conductors of said second printed circuit board beingspaced apart by the same spacing existing between said plurality ofBeryllium Copper conductors on said first printed circuit board; saidfirst printed circuit board being oriented with said plurality ofBeryllium Copper conductors directly facing and aligned with respectiveones of said plurality of metal conductors on said second printedcircuit board; clamping means for mechanically pressing said firstprinted circuit board against said second printed circuit board whereinsaid spring fingers of said first printed circuit board respectivelyengage and compress against corresponding metal conductors on saidsecond circuit board and maintains positive contact pressure on saidcorresponding metal conductors at cryogenic temperature, said clampingmeans including: a first clamping bar and a second clamping bar; saidfirst clamping bar for abutting a rear surface of said first printedcircuit board and said second clamping bar for abutting a rear surfaceof said second printed circuit board; and first and second bolt meansfor extending through said alignment holes and joining said clampingbars; flex cable means having an end, said flex cable means containing aplurality of electrical lines arranged in parallel along a common planesandwiched between first and second covering layers of electricalinsulating material; said second covering layer extending to apredetermined distance of said end, leaving an end portion of saidelectrical lines uncovered; said end portion of said electrical linesoverlaying portions of and being mechanically and electrically connectedto corresponding ones of said spaced metal conductors on said secondprinted circuit board for providing electrical contact with saidrespective corresponding ones of said spaced metal conductors of saidsecond printed circuit board; said second printed circuit board furtherincluding first and second strain relief bolt passages, said first andsecond strain relief bolt passages being spaced apart; strain reliefclamping means for clamping said flex cable to said second printedcircuit board, said clamping means being mounted over said flex cablemeans and before said end portion of said flex cable means; said strainrelief clamping means comprising: a first strain relief clamping bar anda second strain relief clamping bar; said first strain relief clampingbar including a pair of bolt passages, said bolt passages being spacedapart the same distance as said first and second strain relief boltpassages; said second strain relief clamping bar including a pair ofthreaded bolt holes, said bolt holes being spaced apart the samedistance as said first and second strain relief bolt passages; saidfirst strain relief clamping bar for abutting said flex cable and saidsecond strain relief clamping bar for abutting a rear surface of saidsecond printed circuit board; first strain relief bolt means forextending through one of said pair of bolt passages in said first strainrelief clamping bar, said first strain relief bolt passage, and intothreaded engagement with one of said pair of threaded bolt holes; andsecond strain relief bolt means for extending through another one ofsaid pair of bolt passages in said first strain relief clamping bar,said second strain relief bolt passage, and into threaded engagementwith another one of said pair of threaded bolt holes.